A typical apparatus for cleaning a fluid medium, particularly for cleaning fuel and in which solid particulates and fluid components of greater density are separated from fluid components of lesser density, has a housing having at least one inlet port for the fluid medium to be cleaned and at least one outlet port for the cleaned fluid medium. Such an apparatus is used for cleaning fuels, preferably diesel fuels. The fluid components of greater density to be separated from the fluid medium, more particularly from the fuel/diesel fuel, are especially water to be separated out. The fuel, more particularly diesel fuel, cleaned in the apparatus is subsequently fed to a consumer, particularly an engine, more particularly an automobile engine.
Various versions of an apparatus of the type described above are known from practice. Such an apparatus is described, for example, in U.S. Pat. No. 5,078,875 and US 2006/0180527. These apparatuses have categorically proven their worth. However, many of the apparatuses of the type mentioned above and known from practice have certain drawbacks. Up to 12% air can dissolve in diesel fuel at room temperature. In the event of a drop in pressure, at least a portion of this gas, more particularly air, outgases. In most of the apparatuses known from practice, the air cannot pass through a filter subassembly provided in the apparatus and accumulates upstream of the filter subassembly. Only once the resulting pressure is sufficiently high can larger quantities of air temporarily pass through the filter subassembly. That is disadvantageous inter alia with regard to the proper functioning of the filter subassembly. Another drawback of the apparatuses known from practice is that, at temperatures below −5° C., components of the diesel fuel flocculate and can clog the filter subassembly. The flocculated components generally melt again only starting at a temperature of 20° C. As a result, the known apparatuses have room for improvement.